The disclosure of Japanese Patent Application No. 2001-231578 filed on Jul. 31, 2001 and No. 2001 filed on Sep. 4, 2001, including the specifications, drawings and abstracts thereof, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a technology for controlling emissions from an internal combustion engine.
2. Description of the Related Art
Emissions from diesel engines normally include particulate substances such as black smoke (soot) and the like, nitrogen oxides, etc. Lately, there is a strong demand for the control of air pollutant emissions. Therefore, in general, diesel engines are equipped with emission control apparatuses for purifying exhaust emissions.
An emission control apparatus described in Japanese Patent Application Laid-Open No. 7-189656 employs a filter (trapper) for occluding particulate substances in exhaust gas. When exhaust particulate substances are occluded and deposit in the filter, the emission control function of the filter is inhibited, so that it is necessary to recover the emission control function of the filter. The filter is loaded with an oxidation catalyst. Exhaust gas flows into the filter alternately via its opposite side surfaces. The emission control function of the filter is recovered through combustion of particulate substances depending on the exhaust gas temperature. A related-art technology for recovering the filter""s emission control function is disclosed in which a filter is loaded with a platinum-group metal and an alkaline-earth metal oxide, and particulate substances occluded by the filter are burned through the use of the temperature of exhaust gas from a diesel engine (in Japanese Examined Patent Application Publication No. 7-106290).
However, the above-described apparatus throttles the intake to the diesel engine in order to raise the exhaust gas temperature. Therefore, during the operation of recovering the emission control function, the operational condition of the diesel engine is forcibly changed. That is, there are cases where the emission control function of the filter cannot be sufficiently recovered in accordance with the engine operation condition required at the time of execution of a normal operation.
The foregoing problem arises not only in the case where the emission control apparatus purifies particulate substances in exhaust gas, but also in the case where the apparatus purifies other air pollutants.
The problem is not limited to diesel engines, but is common to internal combustion engines including, for example, generally termed direction injection gasoline engines in which gasoline is directly injected into the combustion chambers.
The invention has been accomplished in order to solve the aforementioned problems of the related art. It is an object of the invention to provide a technology capable of recovering the emission control function of an emission control apparatus independently of the operational condition of the internal combustion engine.
Described below will be means for achieving the object, and operation and advantages of the means.
In accordance with an aspect of the invention, an emission control apparatus that is applied to an internal combustion engine having a combustion chamber, and that controls emissions discharged from the combustion chamber, includes: an exhaust passage that conveys an exhaust gas discharged from the combustion chamber, and that includes a trunk passage, and a loop passage having a first partial loop passage and a second partial loop passage that branch from the trunk passage; and a path change portion that is provided in a connecting portion between the trunk passage and the loop passage, and that includes a switching valve that is set in a first state where exhaust gas in the loop passage is caused to flow through the first partial loop passage and the second partial loop passage in that order, and is set in a second state where exhaust gas in the loop passage is caused to flow through the second partial loop passage and the first partial loop passage in that order. A first emission control portion is provided in the loop passage, and has a filter that occludes and purifies at least a particulate substance present in the exhaust gas. One side face of the filter communicates with the first partial loop passage, and another side face of the filter communicates with the second partial loop passage. A second emission control portion is provided in the trunk passage downstream of the path change portion, and purifies at least a specific gaseous substance present in the exhaust gas. The emission control apparatus further includes: a recovery agent injection portion that injects a recovery agent for recovering an emission control function of the first emission control portion and an emission control function of the second emission control portion, into at least one of the first partial loop passage and the second partial loop passage; and a control portion that controls injection of the recovery agent.